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ISSN: 2381-8719 Research Article

Delineation of Gold Mineral Potential Zone Using High Resolution Aeromagnetic Data Over Part of Kano State, Nigeria Eshimiakhe Daniel*, Raimi Jimoh and Kola Lawal Ahmadu Bello University, Zaria, Nigeria

ABSTRACT The study of the geometry and kinematics of deep geological structures, bearing mineralization has advanced greatly by the aggressive progress of geophysical techniques over the last decades. The mineralization zones located in the Shanono local government area of Kano state Nigeria has its genesis controlled by shear zones. This research was aimed at delineating and characterizing subsurface geologic structures around the study area. Both qualitative and quantitative analysis of aeromagnetic data has provided defined distinct pattern of the magnetic signatures. Euler solution of the aeromagnetic data with structural index one, revealed the presence of the major tectonic trends of anomalies in the NE-SW and NW-SE directions. The trends of few of these structures are observed to be similar to fracture orientations in the Nigerian basement complex. These structures control the emplacement of the gold mineralization as these provides the pathways to flow of mineral rich fluid within the host rocks of the study area. Keywords: Gold; Fractures; Lineaments

INTRODUCTION dangerous conditions in the absence of the required safe mining regulations to safeguard the operations [5]. The environmental and Nigeria has been known to have a long history of mining and the health implication of mining have long been studied and scientific country was a prominent exporter of minerals such as tin, coal, and literature is full of documented cases of damage to the environment kaolin. Gold is generally found in Nigeria as alluvial and eluvial and human health directly linked to the mining-related pollution [8- placers and primary veins from several parts of supracrustal (schist) 12]. Despite the dangers that this mining activities causes, artisanal belts, in the northwest and southwest of the country [1]. Several gold mining operation continue to spread due to the unattractive authors have studied the gold mineralization in Nigeria and the nature of other means of livelihoods such as farming and fishing host rocks [2,3]. The most occurrences of such gold minerilization in the rural areas where such mineral exists [13]. These dangers are found in the Maru, Anka, Malele, Tsohon Birnin Gwari-Kwaga, have led to the advanced use of geophysical methods to delineate Gurmana, Bin Yauri, Okolom-Dogondaji and Iperindo areas, all fault lines associated with minerals, so as reduce the environmental associated with the schist belts of northwest and southwest Nigeria damages caused by artisanal miners. [1]. All these areas are spatially related to the two fault systems in the region [4] the gold-bearing veins, reefs and stringers are Geophysical techniques (gravity, magnetics and electromagnetics often localized by brittle and ductile fault structures or planes of etc.) have been widely used to get subsurface information of the schistosity that traverse phyllites, schists, quartzites, gneisses and Earth, without engaging in invasive digging. It has been utilized contact aureoles of granitoid masses. to solve many problems such as geotechnical, and exploration etc. The basic step is first to identify the physical property, that is, Artisanal mining in Nigeria, has being a means of livelihood diagnostic of the sought geologic structure in the area of study. The adopted primarily in rural areas [5]. This is sometimes called appropriate geophysical survey is then employed, then field data the informal sector, which is outside the legal and regulatory are acquired and plotted. In some cases, the information needed framework [6]. When not properly done, artisanal mining can be to solve the problem may be obtained directly from these plots, but viewed negatively by governments and environmentalists, because in most cases, more information about the subsurface is required. of its potential for environmental damage, social disruption, and conflicts [7]. Most of these miner’s work in very difficult and often Geophysics has been evolving, and new methods of automating

*Correspondence to: Eshimiakhe Daniel, Ahmadu Bello University, Zaria, Nigeria, E-mail: [email protected] Received: September 12, 2019; Accepted: October 4, 2019; Published: October 11, 2019 Citation: Daniel E, Jimoh R, Lawal K (2019) Delineation of Gold Mineral Potential Zone Using High Resolution Aeromagnetic Data Over Part of Kano State, Nigeria, J Geol Geophys 8:464. 10.35248/2381-8719.464 Copyright: © 2019 Daniel E, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

J Geol Geophys, Vol. 8 Iss. 4 No: 464 1 Daniel E, et al. OPEN ACCESS Freely available online geophysics, such as resistivity, magnetometry, very low frequency, Geology of the study area gravity and seismology, are being developed. The study of the Shanono local government area of Kano state lies on the Basement earth’s magnetic field, is one of the oldest branches of geophysics. Complex rocks of northern Nigeria (Figure 2). The Nigerian It has been known for more than three centuries that the earth basement complex is made up of gneisses, migmatites, and behaves as a large and somewhat irregular magnet [14]. However, metasediments of Proterozoic age which have been intruded by a the ground magnetic is always being studied for precise mapping so series of granitic rocks of Late Precambrian to Lower Palaeozoic as to understand the subsurface geology of an area. This technique age. These rocks have been variably metamorphosed and granitized basically requires measurements of the amplitude of magnetic through at least two tectonic-metamorphic cycles converted to components at discrete points along traverses distributed regularly migmatites and granite-gneiss [18,19]. Falconer et al. have reported throughout the survey area of interest. the occurrence of rocks of the Younger Granites series [20], which Aeromagnetic survey is carried out using a magnetometer on board are Jurassic in age, as well as volcanic, and occasional younger dikes. or towed behind an aircraft, a ship or Boat. The principle is different Nigerian schist belts are complexly deformed with earlier folds as compared to a ground magnetic survey carried out with a hand- being refolded by later once and there are some similarities of the held magnetometer in the sense that it covers much larger areas dominant deformations in all the belts [21]. The Kazaure schist of the earth’s for regional reconnaissance. The airborne magnetic belt is characterized by upright isoclinal folds with NNE-SSW axial survey has been used so well in the mineral exploration industry, planes and well-developed cleavage formed during the Pan-African basically for the characterization of mineralization zones in most orogeny, and relict recumbent isoclinal folds with N-S trending parts of the world and as the secondary tool in gold exploration axial plane mostly obliterated [21]. The Malumfashi schist belt is in Nigeria [15,16]. The success of this method is derived from the characterized by an early ENE-WSW foliation largely obliterated, unique signatures that are produced by the mineralization zones and Pan-African orogenic imprints of light to isoclinal ENE-WSW making it possible to distinguish them from the host rock. folds with N-S axial plane [22]. The role of aeromagnetic method in mineral exploration varies Gold mineralization in the study area occurs in a variety of host from delineation structures like faults, folds, contacts, shear zones rocks, but is generally related to the supracrustal schist belts. and intrusions to automated detection of porphyry and favorable areas of ore deposits. There are various enhancement techniques MATERIALS AND METHODS that can help achieve objectives. Data source Location, climate and vegetation of the study area Four high-resolution aeromagnetic maps (HRAM) were acquired The Shanono local government area lies on latitudes 11.962 N to from the Nigerian Geological Survey Agency (NGSA). These 12.264 N and longitudes 7.979 E to 7.980 E (Figure 1) which is sheets include; sheets 56 (Yashi), 57 (Shanono and Bichi), 79 north-east of Kano state, Nigeria. The inhabitants are agrarian, (Malumfashi) and 80 (Karaye). The aeromagnetic data collected by however, with the discovery of traces of minerals at Shanono, they the NGSA between 2005 and 2009 at a flight altitude of 80 m embrace artisanal mining for gold in the dry season to complement along a series of NE–SW flight lines with a spacing of 500 m. The farming. According to Olofin [17], the climate of Kano state is data were made available in the form of a contoured map on a scale the tropical wet and dry type, although some climate changes are of 1:100,000 grid file. The grid after been superimposed together, believed to have occurred. The natural vegetation of Shanono local extend from 110 30’ N-120 30’ N and from 70 30’ E-80 30’ E, covering government area is the Sudan Savannah type.

Figure 1: Map showing the location of the study area and environment (Adamu, 2018).

J Geol Geophys, Vol. 8 Iss. 4 No: 464 2 Daniel E, et al. OPEN ACCESS Freely available online

Figure 2: Geologic map of Kano State.

Figure 3: Total magnetic intensity (TMI) of the study area gridded on the oasis montaj software using a grid cell size of 0.00225 degrees (250 m) with the two black points indicating the study area.

g kk= F  f x , y the study area. The magnetic field intensity ranges from 33901 to ( xy) ( ) 33099 nT (Figure 3). Oasis Montaj. Ver 8.1 was the software used

∞

 −+i  k xk y xy for the processing. = ∫f ( x, y) e dxdy 1 −∞

Analytical signal f xy,= F−1  gkk , ( ) ( xy) The analytic signal technique is based on the use of the first ∞

 ik  x + k y  1 xy = f x, y e dk dk xy derivative of magnetic anomalies to estimate source characteristics 2 ∫ ( ) 4π −∞ and to locate positions of geologic boundaries such as contacts and faults. The forward and inverse 2-D Fourier transform g and f Nabighian [23] developed the concept of 2D analytic signal, or respectively of the magnetic field anomaly, T is given by: energy envelope, of magnetic anomalies. The amplitude of the 3D

J Geol Geophys, Vol. 8 Iss. 4 No: 464 3 Daniel E, et al. OPEN ACCESS Freely available online analytic magnetic field signal at location (x,y) can be expressed as: RESULT AND INTERPRETATION

22 2 ∂∂∂TTT The contoured digitized data which is referred to as the total Axy ( , ) =  ++ 2 ∂∂∂xxx magnetic field intensity (TMI) was further processed in order to understand the subsurface geological information. It contains both Where, A (x, y) is the amplitude of the analytic signal at (x, y); T is the regional (deeper subsurface) and residual component (shallow the observed magnetic field at (x, y). The purpose of the reduction subsurface). The regional-residual separation filtering technique to the pole is to take an observed total magnetic field map and was used to separate regional, which originates due to deep seated produce a magnetic map that would result, had an area been sources from the residual anomaly, which in turn is associated with surveyed at the magnetic pole. the shallow subsurface geological sources (Figure 4). Euler deconvolution The residual magnetic intensity (RMI) grid was continued to 250 The objective of the 3D Euler deconvolution process depth m to see deeper signature coming from deeper structures (Figure estimations of geologic sources of magnetic or gravimetric 5). This process has smoothened the high frequency shallow anomalies in a two-dimensional grid [24]. The method makes use subsurface features. of a structural index in addition to producing depth estimates. In First and second vertical derivatives (1VD and 2VD) maps were combination, the structural index (SI) and the depth estimates derived from residual magnetic anomaly (derived from upward have the potential to identify and calculate depth estimates for continuation). This procedure enhances the enhance shallow a variety of geologic structures such as faults, magnetic contacts, structures. Figure 6 shows the first vertical derivative, indicating an dikes, sills, etc. Usually, Euler deconvolution assumes a tentative anomalous fault line trending towards the study area. SI and estimates four parameters, such as base level, horizontal and vertical positions of an isolated and single-point geologic source. The second vertical derivative image usually tends to reveal The algorithm uses a least squares method to solve Euler’s equation more deep-seated features (Figure 7). The 2VD image, shows the simultaneously for each grid position within a sub-grid (window). A basement complex rocks as pockets of intrusive structures displayed square window of predefined dimensions (number of grid cells) is in blue pattern. The magmatic induced patterns in the study area moved over the grid along each row. are observed and are accompanied by numerous linear features. Within the study areas, it can be seen that high density of these The Euler’s homogeneity relation could be written in the form linear structures indicating intense structural perturbation during ∂∂TT ∂ T X− X +− Y Y + Z − Z = NB − T 3 emplacement. ( 00) ( ) ( 0) ( ) ∂∂xy ∂ z The Analytic Signal is carried out so as to understand the variation XY, Z Where ( 00, 0) is the position of a magnetic source whose total of magnetic sources in the study area. Analytic signal maps serve as field T is detected at (x, y, z). The total field has a regional value of a major type of reduction to the pole, because they are not subject B [25]. to the instability that occurs in transformations of magnetic fields

Figure 4: Residual magnetic intensity grid map of the study area gridded on oasis montaj using the minimum curvature method on cell size of 0.00225 degrees (250 m) with the two black points indicating the study area.

J Geol Geophys, Vol. 8 Iss. 4 No: 464 4 Daniel E, et al. OPEN ACCESS Freely available online

Figure 5: RMI grid continued upward to 250 m above the observation point with the Black points indicating the study area.

Figure 6: Map showing the First vertical derivative, with the black points indicating the study area. from low magnetic latitudes. They basically also define source intrusions and the Older Basement rocks. Basic igneous rocks have positions regardless of any remnant magnetization in the sources. a higher magnetic susceptibility than acidic igneous rocks. Figure 8 shows the analytic signal map of the study area, in the Three-dimensional Euler deconvolution was also performed on space domain. The maxima of the magnitude of analytic signal the upward continued aeromagnetic data using standard Euler describes the magnetic contacts between igneous intrusions and the deconvolution (Figure 9). This was basically carried out so as to surrounding basement rocks within the study area. It also depends locate depths to the geological structures on the gridded map. The on the magnetic susceptibility contrast between Younger Granite best clustering solution was gotten using a structural index of 1 (for

J Geol Geophys, Vol. 8 Iss. 4 No: 464 5 Daniel E, et al. OPEN ACCESS Freely available online

Figure 7: The second vertical derivative map, with the black points indicating the study area.

Figure 8: Analytical signal map, showing low amplitude of analytical signal around the lineaments of interest. dike) and 9% depth tolerance for fewer solutions (i.e. the most likely upward continued shaded relief map for effective correlation. solution). Structural Index 1.0, which represents cylindrical shaped Lineament map was created (Figures 10 and 11), showing the long body, was chosen because magnetic field of alkaline intrusions can trends which controls the subsurface structure beneath the study simply and accurately be inferred with cylindrical shaped body. area. In this study, the NE, SW and E-W trends are the dominant The dike model depth solution could be attributed to a fracture trends affecting the area. The lineament map was superimposed which is filled by the material. This material is suspected to be a on the first vertical derivative map, to clearly show the lineament Gold mineral within the fracture. The results were plotted on the trends and also the structures in and around the mining sites.

J Geol Geophys, Vol. 8 Iss. 4 No: 464 6 Daniel E, et al. OPEN ACCESS Freely available online

Figure 9: Plot of Euler depth solution on the upward continued shaded relief map.

Figure 10: Aeromagnetic lineament map of the study area.

DISCUSSION The residual magnetic intensity map was upward continued to 250 m. In physical terms, as the continuation distance is In this research work, an aeromagnetic geophysical technique was increased, the effects of smaller, narrower and thinner magnetic utilized to delineate and characterize subsurface geologic structures bodies progressively disappear relative to the effects of larger in and around the study area. These structures are trending NW- magnetic bodies of considerable depth extent. As a result, upward- SE direction. Residual gravity anomaly, upward continued map, continuation maps give the indications of the main tectonic first/second VD maps and analytical signal map derived from aeromagnetic data characterized the subsurface geologic structures. and crustal blocks in an area. The upward continued grid shows a smoother surface, hence the upward continuation helped to The residual magnetic intensity image shows high magnetic remove noise from the residual data before carrying out other susceptible areas in low magnetic values, while less magnetic enhancement techniques. susceptible areas are depicted as high magnetic values. By removing the regional magnetic anomaly from the measured anomaly, both To observe the near-surface source magnetic features that are the negative and positive residual magnetic intensity values were associated with geological structures, the first vertical derivative obtained. The residual magnetic intensity level in the study area (FVD) filter was applied on the upward continued grid. The colour ranges from 81.9 to 114.0 nT. vertical gradient image of the residual magnetic intensity enhanced

J Geol Geophys, Vol. 8 Iss. 4 No: 464 7 Daniel E, et al. OPEN ACCESS Freely available online

Figure 11: Aeromagnetic lineament map of the first vertical derivative. the image by showing major structural and lithological detail Euler deconvolution technique was applied to the residual which were not obvious in the upward continued image. The first aeromagnetic data of the study area with a structural index of 1.0 vertical derivative also shows linear structures (lineament) across in order to determine depths. The solutions obtained clustered the study area with one passing through the mapped gold mining around the region where the sources were located and this was area and hence may have acted as a conduit through which the gold superimposed on the shaded relief map of the second vertical mineralization flow. derivative. It indicates that the depth ranging between 244.5 m to 1436.0 m in the NE–SE trending lineaments. Second vertical derivative calculations were performed on the aeromagnetic data. The second vertical derivative analysis provides CONCLUSION a means of discriminating local features while suppressing broad and regional structures. This filter has a better resolving power The interpreted aeromagnetic data in this research has characterized than the first vertical derivative and derivative maps can, therefore, the lineament structures which pass through gold mineralization be used to sharpen the edges of magnetic anomalies and to better zones at Shanono local government area of Kano State and its their locations. environs. The major structural anomalies trend along NE-SW and NW-SE directions. Both qualitative (second vertical derivative To know the source positions of the magnetic anomaly regardless and analytic signal) and quantitative (Euler deconvolutions) of direction and remnant magnetization in the sources, the techniques were used in achieving the objectives of this research. analytical signal filter was applied to the upward continued grid. Euler deconvolution solution of the aeromagnetic data also gave The result indicates the amplitude values ranging from 0.02169 the depth estimate ranging from 244.5 m to 1436.0 m. The contact nT/m to 0.15223 nT/m. The zone suspected to be fault zone has model produced shallow depth ranging of 101.3 m to 1495.5 m low magnetic susceptibility values ranging from 0.002549 SI to while the dike model, on the other hand, produced depth range of 1.654578 SI. This could be attributed to the mineralization of gold 435.7 m to 2411.9 m for the five selected profiles. This is because discovered in the study area. The delineated linear structure (NE– SE trends) suspected to have acted as a conduit through which gold dike model anomaly occurs at a greater depth than the contact mineralization flows and deposit in the study area, occupies an area model. The contact model seems to best fit the study area since of low amplitude of analytical signal and these agree with Gunn et the delineated structures/lineaments of interest occur at a shallow al. [26], who stated that low magnetic zones are interpreted to have depth. Magnetic susceptibility values range from 0.0000987 to resulted from possible mineral deposits. Gold is among minerals 22.483055 SI units for the five selected profiles. considered to be very low in magnetite content. High magnetic ACKNOWLEGEMENT susceptibility contrasts are also observed in other portions of the map which are possibly due to outcrops in the study area. High The author wishes to thank Dr. Raimi Jimoh of the Department magnetic susceptibilities are normally found in bodies associated of Physics, Ahmadu Bello University, Nigeria for his support and with basic crystalline rocks such as basalt, granite, gneiss, and schist. guidance throughout the research.

J Geol Geophys, Vol. 8 Iss. 4 No: 464 8 Daniel E, et al. OPEN ACCESS Freely available online REFERENCES 15. Ojo A. Geomagnetic and geoelectric investigation of mineral rocks at Awo, Osun State, southwest Nigeria. Int J Phys Res. 2013;1:60–74. 1. Garba I. Geochemical characteristics of mesothermal gold mineralisation in the Pan-African (600±150 Ma) basement of Nigeria. 16. Graham KM, Preko K, Wemegah DD, Boamah D. Geological and J App Earth Sci. 2003;112:319-325. Structural Interpretation of Part of the Buem Formation, Ghana, Using Aero geophysical Data. J Environ Earth Sci. 2013;4:17-31. 2. Woakes M, Bafor BE. Primary gold mineralization in Nigeria. Ingold. 1984;82:661-671. 17. Olofin EA . Some aspects of the physical geography of the kano region and related human responses. departmental lecture note series no. 1 3. Garba I. Gold prospect of the Nigerian Pan-African terrain of West geography department Bayero University, Kano (BUK). 1987. Africa. J Min Geol. 2000;36:123-126. 18. McCurry P. Pan-African orogeny of Northern Nigeria. Bulletin Geol 4. Ramadan TM, Fattah MF. Characterization of gold mineralization in Soc American.1971;82:351-362. Garin Hawal area, Kebbi State, NW Nigeria, using remote sensing. J Remote Sens Space Sci. 2010;13:153-163. 19. Hazell JRT, Cratchley CR, Preston AM. The Location of aquifers in crystalline rocks and alluvium in Northern Nigeria using combined 5. https://content.sph.harvard.edu/mining/files/Veiga.pdf electromagnetic and resistivity techniques. Q J Eng Geol. 1988;21:159. 6. Azubike AL. The Technology of peaty soils in Mozambique and 20. Falconer JD, Longbottom A, Woods H. The geology and geography of Angola: In transactions of the 5th International Congress of Soil northern Nigeria. Macmillan and Company Limited. 1911. Science, Leopoldville. 2011;3:398-401. 21. Danbatta UA. Tectonic significance the nne continuation of kalangai 7. Opafunso ZO. Overview of Artisanal and small scale mining of gold fault zone into the kazaure schist belt of Northwestern Nigeria. operations in Nigeria. Lecture at Federal University of Technology, Africana. 2003;2:17-25. Akure, Ondo State, Nigeria. 2011. 22. McCurry P. The Geology of the precambrian to lower paleozoic rocks 8. Kelly M. Mining and the freshwater environment. Elsevier Science of Northern Nigeria: A review in Kogbe CA. Geology of Nigeria. Publishers, London. 1988. p.231. Elizabethan Publ Co Lagos. 1976:13-37. 9. Thornton I. Impacts of mining on the environment; some local, 23. Nabighian MN. Toward a three-dimensional automatic interpretation regional and global issues. Appl Geochem. 1996;11:355-361. of potential field data via generalized hilbert transforms: Fundamental 10. Dudka S, Adriano DC. Environmental impacts of metal mining and relations. Geophys. 1984;49:780-786. processing: A review. J Environ Qual. 1997;26:590-602. 24. Reid AB, Allsop JM, Granser H, Millet AJ, Somerton IW. Magnetic 11. https://researchonline.jcu.edu.au/3243/ interpretation in three dimensions using Euler deconvolution: Geophys.1990;55:80-91. 12. Plumlee GS, Morman SA. Mine wastes and human health. Elem. 2011;7:399-404. 25. Thomson DT. EULDPTH: A new technique for making computer- assisted depth estimates from magnetic data: Geophys. 1982;47:31-37. 13. Ako TA, Onoduku US, Oke SA, Adamu IA, Ali S E, Mamodu A, et al. Environmental impact of artisanal gold mining in Luku, Minna, Niger 26. Leventhal T, Brooks-Gunn J, Kamerman SB, et al. Communities as State, North Central Nigeria. J Geosci Geomat. 2014;2:28-37. place, face, and space: Provision of services to poor, urban children and their families. Neighborhood poverty: Context and consequences 14. Keating PB. A simple technique to identify magnetic anomalies due to for children. 1997; 13:2. kimberlite pipes. J Explor Mining Crc. 1995;4:121-125

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